2. Contact Info

3. Dealer Selection

Our recent instrumented track results from Dodge‘s super hot Viper GTS ACRplus left us puzzled. What we expected, based on the sheer number of Mopar Performance Parts components installed on this Viper ACR, was stronger acceleration and crisper handling. After all, it sported a “race-calibrated” engine controller ($500), a GTS-R forged-aluminum rocker-arm assembly ($1700), two smooth-bore inlet hoses ($75), stainless racing headers ($3399), a low-restriction, stainless “race” exhaust system ($1675), fully-adjustable aluminum (for jounce and rebound) front and rear shock and spring assemblies ($8010), and a “stronger” ring and pinion set ($325).

So imagine our surprise to find that this car wasn’t quicker and didn’t handle better than stock. Part of the shortcoming can be traced to the less-grippy tarmac at the (not our usual) test venue. It did scorch a 3.9-second 0-60-mph time. But the quarter mile was a “mere” 12.4 at 117.6. Previous GTS Vipers had run 12.1 to 12.2 seconds and from 117.9 to 120.5 mph. Likewise, our 600-foot slalom test also yielded softer numbers than expected. Instead of somewhere around 68.5 to 72.4 mph, the ACRplus carved through at “just” 68.1 mph.

Fortunately, answers arrived the day after the test in a mail package listing the ACRplus’ specs and from a short phone call to Mopar’s experts. First, what we actually got despite the long list of engine parts was an only modest bump of 56 horses and 41 extra pound-feet of torque. A “stock” GTS Viper already makes an incredible 450 horsepower and about 490 pound-feet of torque. The second, but probably most important, factor in our just so-so quarter-mile times was the shorter 3.73:1 “performance” rear axle. Although it might have provided a nice advantage in a parking lot autocross, the shorter gear was causing the engine to hit the rev limiter at about 115 mph in third gear-just shy of a full quarter mile. (Note that the standard axle is a much taller 3.07.) The driver’s choices were to run up against the limiter or attempt a quick upshift. Unfortunately, both strategies blunted quarter-mile times and speeds.

What about the slower pass through the slalom? The experts at Mopar disclosed that the car’s adjustable shocks had been left on their softest settings. The result was a great riding Viper, but also a measurable loss in response. A few up clicks on the adjusters would’ve sharpened the car’s response.

In the end, the real benefit provided by the Mopar’s premium shocks was to ride comfort.

The shorter axle ratio does make the Viper’s response even fiercer for timed handling events. At the dragstrip, however, the standard axle works best. The lesson: Do your homework carefully before you shop for parts or test a car. Otherwise, you may find performance improved, just not in the targeted area.

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